Hearing aids with adaptive beamformer responsive to off-axis speech

ABSTRACT

A hearing assistance system includes an adaptive directionality controller to control a target direction for sound reception. The adaptive directionality controller includes a beamformer, a speech detector to detect off-axis speech being speech that is not from the target direction, and a steering module to steer the beamformer in response to a detection of the off-axis speech.

CLAIM OF PRIORITY

The present application claims the benefit under 35 U.S.C. §119(e) ofU.S. Provisional Patent Application Ser. No. 61/582,086, filed on Dec.30, 2011, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This document relates generally to hearing assistance systems and moreparticularly to hearing aids having adaptive directionality usingbeamformer responsive to detection of off-axis speech.

BACKGROUND

Hearing aids are used to assist people suffering hearing loss bytransmitting amplified sounds to their ear canals. Damage of outer haircells in a patient's cochlear results loss of frequency resolution inthe patient's auditory perception. As this condition develops, itbecomes difficult for the patient to distinguish speech fromenvironmental noise. Simple amplification does not address suchdifficulty. Thus, there is a need to help such a patient inunderstanding speech in a noisy environment.

SUMMARY

A hearing assistance system includes an adaptive directionalitycontroller to control a target direction for sound reception. Theadaptive directionality controller includes a beamformer, a speechdetector to detect off-axis speech being speech that is not from thetarget direction, and a steering module to steer the beamformer inresponse to a detection of the off-axis speech.

In one embodiment, a hearing assistance system for transmitting soundsinto one or more ear canals includes a plurality of microphones toreceive sounds, one or more receivers to deliver processed sounds to theone or more ear canals, and a processor coupled between the plurality ofmicrophones and the one or more receivers to process the receivedsounds. The processor includes an adaptive directionality controller tocontrol a target direction. The adaptive directionality controllerincludes a beamformer, a speech detector, and a steering module. Thebeamformer cancels received sounds that are not from the targetdirection by beamforming. The speech detector detects off-axis speechbeing speech that is not from the target direction. The steering modulesteers the beamformer in response to a detection of the off-axis speechto reduce cancellation of the off-axis speech by the beamformer.

In one embodiment, a method is provided for adaptive control of a targetdirection of sound reception by a hearing assistance system using abeamformer. Off-axis speech is detected. The off-axis speech is a speechthat is not from the target direction. In response to a detection of theoff-axis speech, the beamformer is steered to reduce cancellation of theoff-axis speech by the beamformer.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of a hearingassistance system having adaptive directionality control.

FIG. 2 is a block diagram illustrating an embodiment of the hearingassistance system including a mononaural hearing aid having the adaptivedirectionality control.

FIG. 3 is a block diagram illustrating an embodiment of the hearingassistance system including a pair of binaural hearing aids having theadaptive directionality control.

FIG. 4 is a flow chart illustrating an embodiment of a method foroperating a hearing assistance system with adaptive directionalitycontrol.

FIG. 5 is a flow chart illustrating another embodiment of a method foroperating a hearing assistance system with adaptive directionalitycontrol.

FIG. 6 is a flow chart illustrating an embodiment of an algorithmimplementing the method of FIG. 5.

FIGS. 7-10 are graphs showing behavior of an off-axis speech detector indifferent scenarios.

FIGS. 7A-C show behavior of the off-axis speech detector for diffusenoise only condition.

FIGS. 8A-C show behavior of the off-axis speech detector for speech at 0degree from a target direction and diffuse noise with a signal-to-noiseratio (SNR) at 10 dB.

FIGS. 9A-C show behavior of the off-axis speech detector for speech at180 degree from the target direction and diffuse noise with an SNR at 10dB.

FIGS. 10A-C show behavior of the off-axis speech detector for speech at180 degree from the target direction and diffuse noise with an SNR at 10dB, with the off-axis speech detector turned on.

FIG. 11 is a graph showing results of using an off-axis speech detectorin improving understanding of speech from a rear source (behind thelistener).

FIG. 12 is a flow chart illustrating an embodiment of a method fordetecting off-axis speech detection during ear-to-ear communication.

FIG. 13 is a flow chart illustrating another embodiment of a method foroperating a hearing assistance system with adaptive directionalitycontrol.

FIG. 14 is a flow chart illustrating an embodiment of an algorithmimplementing the method of FIG. 13.

FIG. 15 is a flow chart illustrating another embodiment of a method fordetecting off-axis speech detection during ear-to-ear communication.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto subject matter in the accompanying drawings which show, by way ofillustration, specific aspects and embodiments in which the presentsubject matter may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent subject matter. References to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.The following detailed description is demonstrative and not to be takenin a limiting sense. The scope of the present subject matter is definedby the appended claims, along with the full scope of legal equivalentsto which such claims are entitled.

This document discusses a hearing assistance system that has adaptivedirectionality provided by a beamformer with off-axis speech detectionand response. The beamformer combines signals of two or more microphonesto amplify sound signals from a target direction while attenuating soundsignals from the other directions. The limited microphone distance andthe limited allowed computational complexity are the main challenges forhearing aids applications. The two or more microphones are in onehearing aid device of a mononaural hearing aid system or both hearingaid devices in a binaural hearing aid system. Adaptive beamformingprovides for determination of the target direction using output of thetwo or more microphones.

Adaptive beamforming algorithms aim to minimize the output of thebeamformer, while maintaining a 0 dB transfer function in the targetdirection, such as discussed in Elko, G. W. and Pong, A. N., “A simplefirst order directional microphone,” Proceedings of the IEEE WorkshopAppl. Signal Process. Audio Acoust, 1995: 169-172. These algorithms donot take into account the nature of the incoming signals. Hence itreduces noise signals as well as speech signals that are not coming fromthe target direction, i.e., off-axis speech signals. Various algorithmshave been developed to address this issue. In one example, an adaptivebeamforming algorithm switches to omnidirectional mode in response todetection of an off-axis speech-like signal, as is done in Starkey'sDynamic Directionality algorithm. However, this requires a discretedetection, and there will be an audible difference going fromdirectional to omnidirectional mode. This is especially problematic whendetection of off-axis speech is intermittent. Changing from thedirectional to omnidirectional mode may also result in changes in thenoise level of up to 5 dB. Thus, frequent mode changes can be annoyingfor the user (listener). In another example, an adaptive beamformingalgorithm uses two adaptive directional microphones to track the mostdominant source without distinguishing between speech and noise, asdiscussed in European Patent No. EP 2 339 574 A1 to Janse et al.,entitled “Speech Detector. European Patent Application”. However, thisrequires two adaptive filters and is unable to distinguish betweenspeech and noise.

The present system detects off-axis speech and steers the beamformeraway from the detected off-axis speech, thereby reducing cancellation ofthe off-axis speech by the beamformer. The aim is to avoid thecancellation of the off-axis speech by the beamformer when the off-axisspeech is detected. The present system does not require discrete modesin the algorithm, and does not substantially change noise level when thebeamformer is steered. Change of location of the null as the beamformeris steered has limited influence (such as about 1 dB) on the experiencednoise level.

The present subject matter is demonstrated for hearing assistancedevices, including hearing aids, including but not limited to,behind-the-ear (BTE), in-the-ear (ITE), in-the-canal (ITC),receiver-in-canal (RIC), or completely-in-the-canal (CIC) type hearingaids. It is understood that behind-the-ear type hearing aids may includedevices that reside substantially behind the ear or over the ear. Suchdevices may include hearing aids with receivers associated with theelectronics portion of the behind-the-ear device, or hearing aids of thetype having receivers in the ear canal of the user, including but notlimited to receiver-in-canal (RIC) or receiver-in-the-ear (RITE)designs. The present subject matter can also be used in hearingassistance devices generally, such as cochlear implant type hearingdevices and such as deep insertion devices having a transducer, such asa receiver or microphone, whether custom fitted, standard, open fittedor occlusive fitted. It is understood that other hearing assistancedevices not expressly stated herein may be used in conjunction with thepresent subject matter.

FIG. 1 is a block diagram illustrating an embodiment of a hearingassistance system 100. Hearing assistance system 100 transmits soundsinto one or more ear canals of a user and includes a plurality ofmicrophones 110, one or more receivers 130, and a processor 120 coupledbetween microphones 110 and receiver(s) 130. Microphones 110 receivesounds. Receiver(s) 130 deliver processed sounds to the one or more earcanals. Processor 120 processes the received sounds and includes anadaptive directionality controller 122. Adaptive directionalitycontroller 122 controls a target direction of sound reception by system100 and includes a beamformer 124, a speech detector 126, and a steeringmodule 128. Beamformer 124 cancels received sounds that are not from thetarget direction by beamforming. Speech detector 126 detects off-axisspeech being speech that is not from the target direction. Steeringmodule 128 steers the beamformer in response to a detection of theoff-axis speech to reduce cancellation of the off-axis speech by thebeamformer.

In various embodiments, processor 120 includes a microprocessor-basedcircuit programmed to perform one or more of the various methodsdiscussed in this document. In various other embodiments, processor 120includes a custom integrated circuit configured to perform one or moreof the various methods discussed in this document. In various otherembodiments, processor 120 includes a combination of generic and customcircuits configured to perform one or more of the various methodsdiscussed in this document.

FIG. 2 is a block diagram illustrating an embodiment of a hearingassistance system 200. Hearing assistance system 200 represents anembodiment of hearing assistance system 100 and includes a mononauralhearing aid 240. Hearing aid 240 includes microphones 110, receiver(s)130, and processor 120.

FIG. 3 is a block diagram illustrating an embodiment of hearingassistance system 200. Hearing assistance system 200 represents anembodiment of hearing assistance system 100 and includes a pair ofbinaural hearing aids, which includes a left hearing aid 340L and aright hearing aid 340R. Left hearing aid 340L includes at least onemicrophone 110L of microphones 110, at least one receiver 130L ofreceiver(s) 130, and a processor 120L including a portion of processor120. Right hearing aid 340R includes at least one microphone 110R ofmicrophones 110, at least one receiver 130R of receiver(s) 130, and aprocessor 120R including a portion of processor 120. In one embodiment,binaural hearing aids 340L and 340R are capable of ear-to-earcommunication, which is controlled by processors 120L and 120R.

FIG. 4 is a flow chart illustrating an embodiment of a method 400 foroperating a hearing assistance system with adaptive directionalitycontrol, such as hearing assistance system 100 and its variousembodiments. In one embodiment, adaptive directionality controller 122is programmed to perform method 400.

At 402, sounds are received by the hearing assistance system. At 404, atarget direction of the sound reception by the hearing assistance systemis controlled using a beamformer. At 406, off-axis speech is detected.The off-axis speech is a speech that is not from the target direction.In response to a detection of the off-axis speech at 408, the beamformeris steered to reduce cancellation of the off-axis speech by thebeamformer at 410. In various embodiments, the beamformer is steeredaway from the detected off-axis speech to minimize the cancellation ofthe off-axis speech by the beamformer at 410.

Flow charts are used in this document to illustrate various methods byway of example, and not by way of restriction. For each flow chart inthis document, the blocks or steps are not necessarily performed in theorder exactly as illustrated, as those skilled in the art willunderstand upon reading this document including the descriptionassociated with each of the flow charts.

FIG. 5 is a flow chart illustrating another embodiment of a method 500for operating a hearing assistance system with adaptive directionalitycontrol. Method 500 represents an embodiment of method 400 and detectsoff-axis speech using output of forward-looking and rearward-lookingcardioids. An example of the output of the forward-looking andrearward-looking cardioids is discussed in Elko, G. W. and Pong, A. N.,“A simple first order directional microphone,” Proceedings of the IEEEWorkshop Appl. Signal Process. Audio Acoust, 1995: 169-172. Theforward-looking cardioid is associated with the current beamformer. Inone embodiment, adaptive directionality controller 122 is programmed toperform method 500.

At 502, a forward signal level and a rearward signal level arecalculated in power domain. The forward signal level is a signal levelof the forward-looking cardioid. The rearward signal level is a signallevel of the rearward-looking cardioid.

At 504, a forward noise level and a rearward noise level are calculatedin power domain. The forward noise level is a noise level of theforward-looking cardioid. The rearward signal level being a noise levelof the rearward-looking cardioid. An example of a technique forcalculating the forward and rearward noise levels is discussed inMartin, R., “Spectral Subtraction Based on Minimum Statistics”,EUSIPCO-94, Edinburgh, Scotland, 13-16 Sep. 1994, pp. 1182-1185.

At 506, a rearward signal-to-noise ratio (SNR), which is the SNR of therearward-looking cardioid, is calculated using the rearward signal leveland the rearward noise level. At 508, the rearward SNR is compared to aspecified threshold SNR. At 510, a detection of off-axis speech isindicated in response to the rearward SNR being larger than thespecified threshold SNR.

At 512, a forward SNR, which is the SNR of the forward-looking cardioid,is calculated using the forward signal level and the forward noiselevel. At 514, the rearward SNR is compared to the forward SNR. At 516,a rear source of the off-axis speech is indicated in response to therearward SNR exceeding the forward SNR by a specified margin. In otherwords, if the rearward SNR is larger than the forward SNR by thespecified margin, the off-axis speech is determined as being from theback of the user (listener).

At 516, the beamformer is steered in response to the rear source beingindicated. In one embodiment, the beamformer is steered by changing avalue of an adaptation speed of the beamformer. In one embodiment, thesign of this value is changed, so that the beamformer adapts away fromthe most dominant source of speech instead of towards the most dominantsource of speech.

FIG. 6 is a flow chart illustrating an embodiment of an algorithmimplementing method 500. MAX_VALUE is the maximum value thatoutputPowerSum and rearPowerSum can have. The parametersoutputNoiseEstimate, outputNoiseEstimateCurrent, rearNoiseEstimate, andrearNoiseEstimateCurrent are initialized to MAX_VALUE.

FIGS. 7-10 are graphs showing measured behavior of an off-axis speechdetector in different scenarios. This off-axis speech detector is animplementation of speech detector 126.

FIG. 7A shows the forward signal level (OutputLevel), the rearwardsignal level (BackwardLevel), the forward noise level (Output Noise),and the rearward noise level (BackwardNoise) for diffuse noise onlycondition. FIG. 7B shows the forward SNR (front) and rearward SNR(rear). The SNRs are below 6 dB for most instances (as expected). FIG.7C shows SNR improvement of using rearward-looking cardioid overforward-looking cardioids (current beamformer). The improvement is below3 dB (as expected).

FIG. 8A shows the forward signal level (OutputLevel), the rearwardsignal level (BackwardLevel), the forward noise level (Output Noise),and the rearward noise level (BackwardNoise) for speech at 0 degree fromthe target direction and diffuse noise with SNR at 10 dB. FIG. 8B showsthe forward SNR (front) and rearward SNR (rear). The forward SNR isabove the rearward SNR for most instances. FIG. 8C shows SNR improvementof using rearward-looking cardioid over forward-looking cardioids(current beamformer). The improvement is below 3 dB. The maximumimprovement is observed when there is no speech.

FIG. 9A shows the forward signal level (OutputLevel), the rearwardsignal level (BackwardLevel), the forward noise level (Output Noise),and the rearward noise level (BackwardNoise) for speech at 180 degreesfrom the target direction and diffuse noise with SNR at 10 dB, with theoff-axis detector turned off. FIG. 9B shows the forward SNR (front) andrearward SNR (rear). The rearward SNR is above the forward SNR for mostinstances. The forward SNR gets worse as speech increases. FIG. 9C showsSNR improvement of using rearward-looking cardioid over forward-lookingcardioids (current beamformer). The improvement is above 3 dB whenspeech is present.

FIG. 10A shows the forward signal level (OutputLevel), the rearwardsignal level (BackwardLevel), the forward noise level (Output Noise),and the rearward noise level (BackwardNoise) for speech at 180 degreesfrom the target direction and diffuse noise with SNR at 10 dB, with theoff-axis detector turned on. FIG. 10B shows the forward SNR (front) andrearward SNR (rear). The rearward SNR is higher than the forward SNR formost instances. The forward SNR gets worse as speech increases. FIG. 10Cshows SNR improvement of using rearward-looking cardioid overforward-looking cardioids (current beamformer). The improvement is above3 dB when speech is present. When the off-axis speech detector is turnedon, the forward SNR (FIG. 10B, “front”) is substantially higher than theforward SNR (FIG. 9B, “front”) when the off-axis speech detector isturned off. The improved forward SNR is proof that the off-axis speechdetector protects the speech.

The values of beta (beamformer coefficient) as function of time andfrequency for speech at 180 degrees from the target direction anddiffuse noise with SNR at 10 dB, with the off-axis speech detectorturned on and off, are measured. When the off-axis speech detector isturned off, beta goes towards 0 (180 degrees). When the off-axis speechdetector is turned on, beta goes towards 1 (90 degrees).

The off-axis speech detector, as the implementation of speech detector126, has been tested in a clinical evaluation. A Connected Speech Test(CST) was done with noise from all angles and speech from 0 degree, 135degrees, and 225 degrees. FIG. 11 is a graph showing results of usingthe off-axis speech detector in improving understanding of speech from arear source, i.e., behind the user (listener), as desired. In FIG. 11,CST performance is plotted as function of angle of inciding speech forthe off-axis speech detector turn off (Off) and on (On).

When adaptive directionality is enabled in a pair of binaural hearingaids, such as left hearing aid 340L and right hearing aid 340R, afurther enhancement can be made by linking the functionality throughear-to-ear communication. An example of research on preferenceevaluation reached the following conclusions: (1) preference is basedprimarily on the location of the speech signal, with background noiselocation as a secondary consideration, and (2) maintaining some signalaudibility, even when listening comfort is the primary goal, is aconsistent and recurring theme. This research emphasizes the use of theoff-axis speech detector, because it preserves the speech. In a binauralsystem, however, the information of two sides can be used to improve it.

FIG. 12 is a flow chart illustrating an embodiment of a method fordetecting off-axis speech detection during ear-to-ear communication. Ina non-ear-to-ear mode, the off-axis speech detector of each of thehearing aids works independently to preserve speech as good as possible.When the ear-to-ear communication is enabled, it is possible to detectwhich side is closer to the speech and have that side focus on thespeech and the other side focus on providing comfort, if the input levelis higher than a certain threshold. This idea is illustrated in the flowchart of FIG. 12, which represents part of an example of an ear-to-earcommunication algorithm. Each hearing aid estimates a (long-term) localmode of the directionality: omnidirectional, adaptive, or off-axisspeech. The hearing aids exchange the two local modes. If one of thehearing aids has an omnidirectional mode, both hearing aids will go toomnidirectional. If both hearing aids are in the adaptive or off-axisspeech modes, both hearing aids will go to the adaptive or off-axisspeech modes. If one hearing aid is in the off-axis speech mode and theother hearing aid is in the adaptive mode, the hearing aid in theoff-axis speech mode is closer to the speech. The other hearing aid willdisable its short-term off-axis speech detection if the input level isabove a certain threshold, because the user would prefer listeningcomfort over intelligibility at high input levels.

FIG. 13 is a flow chart illustrating an embodiment of a method 1300 foroperating a hearing assistance system with adaptive directionalitycontrol. Method 1300 represents another embodiment of method 400 anddetects off-axis speech using output of the forward-looking andrearward-looking cardioids. The forward-looking cardioid is associatedwith the current beamformer. In one embodiment, adaptive directionalitycontroller 122 is programmed to perform method 1300.

At 1302, an alternative beamformer is created at an angle away from anormal (current) beamformer. In one embodiment, this alternativebeamformer is created by producing a signal by multiplying arearward-looking cardioid signal with a coefficient betaDiff, whichcorresponds to a specified angle away from an actual (normal) beamformercoefficient beta, and subtracting the produced signal from aforward-looking cardioid signal to result in an alternative beamformersignal.

At 1304, an alternative signal level and a normal signal level arecalculated in power domain. The alternative signal level is a signallevel of the alternative beamformer. The normal signal level is a signallevel of a normal beamformer.

At 1306, an alternative noise level and a normal noise level arecalculated in power domain. The alternative noise level is a noise levelof the alternative beamformer. The normal noise level is a noise levelof the normal beamformer. An example of a technique for calculatingthese noise levels is discussed in Martin, R., “Spectral SubtractionBased on Minimum Statistics”, EUSIPCO-94, Edinburgh, Scotland, 13-16Sep. 1994, pp. 1182-1185.

At 1308, an alternative SNR is calculated using the alternative signallevel and the alternative noise level, and a normal SNR is calculatedusing the normal signal level and the normal noise level. Thealternative SNR is the SNR of the alternative beamformer. The normal SNRis the SNR of the normal beamformer.

At 1310, the alternative SNR is compared to a specified threshold SNR.At 1312, the alternative SNR is compared to the normal SNR in responseto the alternative SNR exceeding the specified threshold SNR. At 1314, adetection of off-axis speech is indicated in response to the alternativeSNR exceeding the normal SNR by a specified margin.

At 1316, the normal beamformer is steered towards the alternativebeamformer in response to the detection of the off-axis speech beingindicated. In one embodiment, this includes adapting the coefficient ofthe normal beamformer towards the coefficient of the alternativebeamformer.

FIG. 14 is a flow chart illustrating an embodiment of an algorithmimplementing method 1300. The rearward-looking cardioid (C) ismultiplied with an alternative coefficient betaDiff and subtracted fromthe forward-looking cardioid. The SNR of the resulting alternativebeamformer is compared to the SNR of the normal beamformer. If the SNRof the alternative beamformer is larger than a threshold, and the SNR ofthe alternative beamformer is higher than the SNR of the normalbeamformer, the off-axis detector detects off-axis speech, and thebeamformer coefficient is adapted to the alternative beamformercoefficient betaDiff.

FIG. 15 is a flow chart illustrating another embodiment of a method fordetecting off-axis speech detection during ear-to-ear communication. Inthis embodiment, the off-axis speech detector reverts to the adaptationdirection in response to a detection of off-axis speech. Hence a newposition of the null of the beamformer will depend on the currentposition of the null and the position of the detected off-axis speech.The null may go to different angles for different frequencies.

In the illustrated embodiment, when the ear-to-ear communication isused, the information of both hearing aids is used to estimate theposition of the off-axis speech, and the null is moved away from thatposition. The hearing aids estimate the SNR of the rearward-lookingcardioid at high frequencies. The hearing aid with the highest SNR iscloser to the source of the off-axis speech. The position of the sourceof the off-axis speech is estimated by averaging the value of beta whichindicates the position of the null. This averaged beta value is comparedto a threshold. If the value is above the threshold, the null is steeredtowards 180 degrees from the target direction. If the value is below thethreshold, the null is steered towards 90 degrees from the targetdirection.

Another embodiment (not shown in FIG. 15) uses a beamformer whoseexample is discussed in Warsitz, E. and Reinhold Haeb-Umbach, “Acousticfilter-and-sum beamforming by adaptive principal component analysis,”Acoustics, Speech, and Signal Processing, 2005. Proceedings. ICASSP '05,vol. 4, no., pp. iv/797-iv/800 Vol. 4, 18-23 Mar. 2005. This embodimentrequires transfer of audio (or encoded audio) and synchronized hearingaids.

The present method and system provide the ability to maintainintelligibility of off-axis speech sources without any audibledistortions. Various embodiments of the present method and system may beincluded in adaptive directionality feature of hearing aids.

This application is intended to cover adaptations or variations of thepresent subject matter. It is to be understood that the abovedescription is intended to be illustrative, and not restrictive. Thescope of the present subject matter should be determined with referenceto the appended claims, along with the full scope of legal equivalentsto which such claims are entitled.

What is claimed is:
 1. A hearing assistance system for receiving andprocessing sounds with control of directionality of sound reception,comprising: a processor configured to process the received sounds andincluding an adaptive directionality controller configured to control atarget direction of the sound reception using a beamformer configured tocancel sound signals that are not coming from the target direction, thesound signals including off-axis speech and noise, the adaptivedirectionality controller configured to: detect the off-axis speech; andsteer the beamformer to reduce the cancellation of the off-axis speechwithout substantially changing the cancellation of the noise in responseto a detection of the off-axis speech.
 2. The system of claim 1, whereinthe adaptive directionality controller is programmed to detect theoff-axis speech using output of forward-looking and rearward-lookingcardioids.
 3. The system of claim 1, wherein the adaptive directionalitycontroller is programmed to: calculate a rearward signal-to-noise ratio(SNR), the rearward SNR being the SNR of a rearward-looking cardioid;and detect the off-axis speech using the rearward SNR.
 4. The system ofclaim 3, wherein the adaptive directionality controller is programmedto: compare the rearward SNR to a specified threshold SNR; and indicatethe detection of the off-axis speech in response to the rearward SNRbeing larger than the specified threshold SNR.
 5. The system of claim 3,wherein the adaptive directionality controller is programmed to:calculate a forward SNR, the forward SNR being the SNR of aforward-looking cardioid; compare the rearward SNR to the forward SNR;and indicate a rear source of the off-axis speech in response to therearward SNR exceeding the forward SNR by a specified margin.
 6. Thesystem of claim 1, wherein the adaptive directionality controller isprogrammed to: create an alternative beamformer at an angle away from acurrent beamformer; calculate an alternative signal-to-noise ratio (SNR)and a normal SNR, the alternative SNR being the SNR of the alternativebeamformer, the normal SNR being the SNR of the current beamformer; anddetect the off-axis speech using the alternative SNR and the normal SNR.7. The system of claim 6, wherein the adaptive directionality controlleris programmed to: compare the alternative SNR to a specified thresholdSNR; compare the alternative SNR to the normal SNR in response to thealternative SNR exceeding the specified threshold SNR; and indicate thedetection of the off-axis speech in response to the alternative SNRexceeding the normal SNR by a specified margin.
 8. The system of claim7, wherein the adaptive directionality controller is programmed to steerthe current beamformer towards the alternative beamformer in response tothe detection of the off-axis speech being indicated.
 9. A hearingassistance system for transmitting sounds into one or more ear canals,comprising: a plurality of microphones configured to receive sounds; oneor more receivers configured to deliver processed sounds to the one ormore ear canals; and a processor coupled between the plurality ofmicrophones and the one or more receivers, the processor configured toprocess the received sounds and including an adaptive directionalitycontroller configured to control a target direction, the adaptivedirectionality controller including: a beamformer configured to canceloff-axis sounds of the received sounds, the off-axis sounds being soundsthat are not from the target direction; a speech detector configured todetect off-axis speech of the off-axis sounds; and a steering moduleconfigured to steer the beamformer in response to a detection of theoff-axis speech to reduce the cancellation of the off-axis speechwithout changing the cancellation of noise of the off-axis soundssubstantially.
 10. The system of claim 9, comprising one or more hearingaids including the plurality of microphones, the one or more receivers,and the processor.
 11. The system of claim 10, comprising a mononauralhearing aid including the plurality of microphones, the one or morereceivers, and the processor.
 12. The system of claim 10, comprising apair of binaural hearing aids each including at least one microphone ofthe plurality of microphones, at least one receiver of the one or morereceivers, and a portion of the processor.
 13. The system of claim 10,wherein the one or more hearing aids are each configured as abehind-the-ear (BTE) hearing aid.
 14. The system of claim 10, whereinthe one or more hearing aids are each configured as an in-the-ear (ITE)hearing aid.
 15. The system of claim 14, wherein the one or more hearingaids are each configured as an in-the-canal (ITC) hearing aid.
 16. Amethod for adaptive control of a target direction of sound reception bya hearing assistance system, the method comprising: using a beamformerto cancel off-axis sound signals that are not from the target direction,the off-axis sound signals including noise; detecting off-axis speechfrom the off-axis sound signals; and steering the beamformer to reducethe cancellation of the off-axis speech by the beamformer withoutsubstantially changing the cancellation of the noise by the beamformerin response to a detection of the off-axis speech.
 17. The method ofclaim 16, wherein detecting the off-axis speech comprises detecting theoff-axis speech using output of forward-looking and rearward-lookingcardioids.
 18. The method of claim 16, wherein detecting the off-axisspeech comprises: calculating a rearward signal-to-noise ratio (SNR),the rearward SNR being the SNR of a rearward-looking cardioid; detectingthe off-axis speech using the rearward SNR and a specified thresholdSNR.
 19. The method of claim 18, wherein detecting the off-axis speechfurther comprises: calculating a forward SNR, the forward SNR being theSNR of a forward-looking cardioid; detecting a rear source of theoff-axis speech using the rearward SNR and the forward SNR.
 20. Themethod of claim 16, wherein detecting the off-axis speech comprises:creating an alternative beamformer at an angle away from a currentbeamformer; and detecting the off-axis speech using the alternativebeamformer and the current beamformer.
 21. The method of claim 20,wherein detecting the off-axis speech comprises: calculating analternative signal-to-noise ratio (SNR), the alternative SNR being theSNR of the alternative beamformer; calculating a normal SNR, the normalSNR being the SNR of the current beamformer; and detecting the off-axisspeech using the alternative SNR and the normal SNR.
 22. The method ofclaim 21, wherein steering the beamformer comprises steering the currentbeamformer towards the alternative beamformer in response to theoff-axis speech being detected.